1. Field of the Invention
The present invention is directed to a method for displaying the tip of a medical instrument situated in the body of a patient during a medical interventional procedure by means of an imaging modality methods,
2. Description of the Prior Art
Instruments, for example needles, laparoscopes etc., are introduced through the skin, through small orifices into the body of the patient during medical interventional procedures. The instruments are guided only according to xe2x80x9cfeelxe2x80x9d or with the aid of an imaging diagnostic device, preferably with the aid of a tomography device or ultrasound.
In methods of the above type, the position of a slice of the body of the patient shown in a reconstructed image can be described, for example, by its position relative to the patient and its inclination relative to the longitudinal axis of the patient. As shown in FIG. 1, these parameters should be selected such that the instrument, for example a puncture needle 1 in a slice 2 of the body of the patient shown in a tomogram, can be guided to the desired object or site 3, for example to an organ of the patient. In the corresponding tomogram 4 shown in FIG. 2, it can be seen how the puncture needle 1, or actually its image 1xe2x80x2 is guided to the object 3, or actually to its image 3xe2x80x2. In many cases, however, the instrument 1 cannot be moved as planned in the slice 2 shown in the tomogram, but exits this slice 2 and therefore can no longer be completely shown in the tomogram 4. as shown in the FIGS. 3 and 4.
The probability that the instrument will exit the slice shown in the tomogram can be reduced by the selection of a correspondingly thick slice that, when an X-ray CT device is used, can be realized by correspondingly adjusted diaphragms, by CvE tam superimposing neighbored slices, or by using a special reconstruction algorithm. The resolution of the tomogram, however, is reduced by such measures and the navigation of the instrument around sensitive body structures is made more difficult, or may be impossible. Alternatively, there is the possibility to reproduce a narrow slice and to manually correct the position of the slice shown in the tomogram when the instrument exits the slice, so that the instrument is visible again. This procedure, however, interrupts the work flow of the physician conducting the interventional procedure and is a source of prolongation of the duration of the interventional procedure, thus presenting a higher risk for the patient. This is also valid for other imaging methods.
European Application 0 485 999 discloses a method wherein a sectional plane can be marked in an X-ray shadow image (scanogram) by means of a cursor, with reference to which sectional plane a tomogram (tomographic image) is then reconstructed.
An object of the present invention is to provide a method of the type initially described wherein the danger of not being able to display the instrument by means of the imaging method is reduced, or precluded.
In a first inventive embodiment, this object is achieved in a method for displaying the tip of a medical instrument situated in the body of a patient during a medical interventional procedure by means of an imaging method, including the steps of repeatedly acquiring data for a number of planar slices of the patient during the interventional procedure, subsequently analyzing the data to identify in which of the slices the tip of the instrument is situated, and generating a signal that marks the slice that contains the tip of the instrument.
In this embodiment of the inventive method, because data representing a number of planar slices are acquired and since the slice in which the tip of the instrument is situated is identified, assuming that the planar slices cover a large enough region of the body of the patient, the danger that the instrument will exit the scanned region is minimal in practice. The acquisition of data for the planar slices and the reconstruction of enough images can ensue without problems so that an image resolution required for the particular interventional procedure is achieved.
In a preferred version of this embodiment, only that slice that is identified by the signal produced by the tip of the instrument is reconstructed by means of the imaging method and is displayed at a display unit. Therefore, the information that is initially required for carrying out the interventional procedure is available to the physician.
According to another version of this embodiment, data for the slice that is identified by the signal produced by the tip of the instrument are acquired by means of the imaging method so that the tip of the instrument is situated as a middle slice, among the number of acquired slices, at a start of the interventional procedure. This insures that, if the tip of the instrument deviates from the planned access path, leeway is present that is approximately of the same size in both directions. If an uneven number of slices is acquired, the middle slice is correspondingly oriented toward the planned access path of the instrument with respect to its position and its angle of inclination for this purpose. If an even number of slices is acquired, one of the two middle slices is correspondingly orientedand positioned.
If the tip of the instrument leaves the middle slice, the parameters of the data acquisition are adapted (modified), according to an embodiment, so that the tip of the instrument is currently again situated in a middle slice, i.e. the orientation and positioning of the acquired slices is automatically adapted to the path of the tip of the instrument.
Alternatively a visual indicator or an acoustic indicator can be generated via an output unit when the tip of the instrument leaves the original slice, i.e. when it leaves the currently displayed slice. In this case, the physician can then adapt the guidance of the instrument, or the parameters of the data acquisition, to current situation.
In a second embodiment of the invention, the aforementioned object is achieved in a method for displaying the tip of a medical instrument situated in the body of a patient during a medical interventional procedure by means of an imaging method, including the steps of repeatedly acquiring data from a volume of the body of the patient during the interventional procedure, three-dimensionally reconstructing the data and displaying the resulting three-dimensional data sets, at a display unit as three-dimensional data sets and/or as sections of three-dimensional data sets, i.e. as planar data sets. The three-dimensional data sets and/or the resulting planar data sets are analyzed with respect to the location of the tip of the instrument, whereupon a corresponding signal is generated.
Therefore, not only one tomogram of the planar slice in which the tip of the instrument is currently present is reconstructed, but a three-dimensional data set of the acquired volume of the body of the patient is generated. The conditions for various possibilities of displaying the region of the body of the patient containing the tip of the instrument are thus present.
According to a version of this second embodiment, a subject of the three-dimensional data set that contains the tip of the instrument is preferably displayed at the display unit as a three-dimensional data set and/or as sections of a three-dimensional data set, so that the image information required for carrying out the intervention, for example by selecting appropriate sectional planes from the three-dimensional data sets, is presented to the physician.
In a further version this second embodiment of the invention, a subset of the three-dimensional data set that contains the tip of the instrument is displayed as multi-planar slices, i.e. it is displayed by a number of parallel 2-dimensional slices, which are not necessarily parallel slices. The display of multi-planar slices is a precondition in order to achieve, under all circumstances according to a particularly preferred version of the invention, that the orientation of the displayed slice corresponds to the moving direction of the tip of the instrument. The directions defined by the multi-planar slices then can be used for the selection of the sections from the three-dimensional data set.
In the second embodiment, a visual indicator or an acoustic indicator can be generated via an output unit if the signal that marks the subset of the three-dimensional data set that contains the tip of the instrument originates from a different subset than the currently displayed subset of the three-dimensional data set.
Further, in the second embodiment a subset of the three-dimensional data set in which the tip of the instrument is currently present can be displayed if the tip of the instrument exits the formerly displayed subset of the three-dimensional data set.
In preferred versions of both embodiments of the invention, all data are acquired at the same time for the number of planar slices, or for a volume of the body during the interventional procedure, so that all planar slices, or the entire volume, represent only one point in time per repetition. Preferably, the data acquisition at the same time can ensue by means of an X-ray CT device having a two-dimensional arrangement of detector elements. Alternatively, the data can be acquired by means of a magnetic resonance (MR) device, an ultrasound device or by means of a different imaging modality.